Ali Akbar Velayat said increasing enrichment closer to weapons-grade levels was ‘unanimously agreed upon by every component of the establishment’.
Photograph: Ebrahim Noroozi/AP

A top aide to Iran’s supreme leader says the Islamic Republic is ready to enrich uranium beyond the level set by Tehran’s 2015 nuclear deal, just before a deadline it set on Sunday for Europe to offer new terms to the accord.

A video message by Ali Akbar Velayati included him saying that “Americans directly and Europeans indirectly violated the deal,” part of Tehran’s hardening tone with Europe. European parties to the deal have yet to offer a way for Iran to avoid the sweeping economic sanctions imposed by Donald Trump since he pulled the US out of the accord a year ago, especially those targeting its crucial oil sales.

It comes as America has sent thousands of troops, an aircraft carrier, nuclear-capable B-52 bombers and advanced fighter jets to the Middle East. Mysterious oil tanker attacks near the strait of Hormuz, attacks by Iranian-backed rebels in Yemen on Saudi Arabia and Iran shooting down a US military drone have raised fears of a wider conflict engulfing the region.

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What is Iran's nuclear enrichment cap?

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Under the joint comprehensive plan of action signed in 2015, Iran is only permitted to produce low-enriched uranium. This is uranium that has a concentration of 3%-4% of the isotope U-235. This isotype is a fissile material, which is capable of sustaining a nuclear fission chain reaction.

At this low level of enrichment, it can be used to produce fuel for nuclear power plants. Iran is permitted to stockpile 300kg of it, at an enrichment level capped at 3.67%.

A bomb needs uranium that is up to 90% enriched. Iran’s atomic energy agency has said production of enriched uranium has been quadrupled. The more that uranium is enriched, the faster it is to enrich it further.

Iran argues that it is no longer bound by the cap because of the withdrawal of the US from the agreement, and the reimposition of economic sanctions Donald Trump.

In the video, available on a website for the supreme leader Ayatollah Ali Khamenei, Velayati said that increasing enrichment closer to weapons-grade levels was “unanimously agreed upon by every component of the establishment”.

“We will show reaction exponentially as much as they violate it. We reduce our commitments as much as they reduce it,” said Velayati, Khamenei’s adviser on international affairs. “If they go back to fulfilling their commitments, we will do so as well.”

Under the atomic accord, Iran agreed to enrich uranium to no more than 3.67%, which is enough for peaceful pursuits but is far below weapons-grade levels of 90%. Iran denies it seeks nuclear weapons, but the nuclear deal sought to prevent that as a possibility by limiting enrichment and Iran’s stockpile of uranium to 300kg (661 pounds).

On Monday, Iran and United Nations inspectors acknowledged it had broken the stockpile limit. Combining that with increasing its enrichment levels narrows the one-year window experts believe Iran would need to have enough material to build a nuclear weapon, if it chose to do so.

“This would be a very worrisome step that could substantially shorten the time Iran would need to produce the material needed for nuclear weapons,” said Miles Pomper, a senior fellow at the Middlebury Institute of International Studies’ James Marin Center for Nonproliferation Studies. “Both Iran and the Trump administration should be looking for ways to de-escalate the crisis, rather than exacerbate it.”

It remains unclear to what level Iran will choose to raise its uranium enrichment. However, in his remarks Velayati made reference to 5% enrichment.

“For Bushehr nuclear reactor we need 5% of enrichment and it is a completely peaceful goal,” he said. Bushehr, Iran’s only nuclear power plant, is now running on imported fuel from Russia that’s closely monitored by the UN International Atomic Energy Agency (IAEA).

Outside of Bushehr, higher-enriched uranium could be used for naval ships and submarines, something Iran has said it would want to pursue. Iran’s nuclear chief, Ali Akbar Salehi, said in 2016 that nuclear power plants for naval vessels need uranium enriched to at least 5%.

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What is the Iran nuclear deal?

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In July 2015, Iran and a six-nation negotiating group reached a landmark agreement known as the Joint Comprehensive Plan of Action that ended a 12-year deadlock over Tehran’s nuclear programme. The deal, struck in Vienna after nearly two years of intensive talks, limited the Iranian programme, to reassure the rest of the world that it cannot develop nuclear weapons, in return for sanctions relief.

At its core, the JCPOA is a straightforward bargain: Iran’s acceptance of strict limits on its nuclear programme in return for an escape from the sanctions that grew up around its economy over a decade prior to the accord. Under the deal, Iran unplugged two-thirds of its centrifuges, shipped out 98% of its enriched uranium and filled its plutonium production reactor with concrete. Tehran also accepted extensive monitoring by the International Atomic Energy Agency (IAEA), which has verified 10 times since the agreement, and as recently as February, that Tehran has complied with its terms. In return, all nuclear-related sanctions were lifted in January 2016, reconnecting Iran to global markets.

The six major powers involved in the nuclear talks with Iran were in a group known as the P5+1: the UN security council’s five permanent members – China, France, Russia, the UK and the US – and Germany. The nuclear deal is also enshrined in a UN security council resolution that incorporated it into international law. The 15 members of the council at the time unanimously endorsed the agreement.

On 8 May 2018, US president Donald Trump pulled his country out of the deal. Iran announced its partial withdrawal from the nuclear deal a year later.

The US said its ambassador to international organisations in Vienna, Jackie Wolcott, had requested a special meeting of the IAEA to discuss its “latest, concerning report on the Iran regime’s nuclear program.” That meeting is planned for Wednesday.

Iran’s diplomatic mission to Vienna, where the IAEA is based, called the US move “a sad irony” as America had unilaterally withdrawn from the deal a year ago.